The alae nasi (AN) has been identified as a respiratory muscle of the upper airway that is able to alter nasal resistance and modify airflow to the lungs. Neonates and obligate nose breathers and frequently have spontaneous AN activity (nasal flaring) especially in the first hours of life, during feeding, and as a major clinical sign of respiratory distress. We have shown that AN activation is enhanced during active as compared to quiet sleep, has its onset and peak of activity prior to that of the diaphragm (DIA), and causes a reduction in nasal resistance and consequent decrease in negative pharyngeal pressure during inspiration. As the AN may influence work of breathing and airway patency in newborn infants, it is important to understand the chemical and mechanoreceptor control of this muscle in comparison to that of the DIA. We plan to alter chemosensitivity using brief periods of hypoxemia or hyperoxia alone or in combination with hypercapnia to determine the relative roles of these chemical stimuli on the control of AN and DIA activity. We will alter the level of mechanoreceptor stimulation by means of continuous positive airway pressure and airway occlusion to define the role of stretch receptors in modifying AN activity. The latter studies will be additionally performed both prior to and following extubation to determine the relative roles of receptors in the upper and lower airway. We will characterize the physiologic mechanics underlying the AN activity observed during both non-nutritive sucking and oral feeding. In all these studies, AN activity will be compared to that of the DIA to determine their relative responses to the range of various stimuli. An understanding of the factors that trigger AN activation will allow us to infer the physiologic processes underlying spontaneous nasal flaring in infants. Since numerous respiratory muscles of the upper airway appear to exhibit similar responses to certain stimuli, unstable AN activity might reflect a generalized derangement involving other upper airway muscles. The ready accessibility of the AN to both clinical observations and physiologic measurements could reveal abnormalities in the neuromuscular control of the upper airway in neonates at risk for obstructive apneic episodes.